Polymerization of cast acrylic resins



United States Patent Office 3,442,851 POLYMERIZATION F CAST ACRYLICRESINS Robert J. McManimie, Glendale, Mo., assignor to Monsanto Company,St. Louis, Mo., a corporation of Delaware No Drawing.Continuation-impart of application Ser. No. 423,862, Jan. 6, 1965. Thisapplication Dec. 17, 1965, Ser. No. 514,672

Int. Cl. C08f 1/84, N78 US. Cl. 260-41 16 Claims The present inventionis a continuation-in-part of application of an earlier filed US. patentapplication Ser. No. 423,862, filed Jan. 6, 1965, now Patent No.3,324,074.

This invention relates to a process for preparing polymericcompositions. One specific aspect of the invention relates to a processfor preparing rigid polymeric compositions comprising an alkylmethacrylate polymer and and inorganic material.

The terms reinforcing agent and reinforcing medium apply to inorganicsubstances, subsequently described in detail which are bonded to apolymer through a coupler. This is in distinction to inorganics whichserve as fillers or diluents for a polymer system and are not bound tothe polymer matrix. The terms reinforced polymeric composition andreinforced polymer refer to those compositions comprising a polymer andreinforcing agent wherein the reinforcing agent is bound to the polymerthrough a third component referred to as a coupling agent. A couplingagent is a compound containing two or more reactive groups, at least oneof which is suitable for reaction with the polymer or monomer, and atleast one of which is suitable for reaction with a reinforcing agent.The term granular as used subsequently in this disclosure refers toparticles wherein the smallest and largest dimensions of a singleparticle diifer by no more than a factor of about five. The termacicular refers to particles having a length over diameter ratio (l/ d)of from five to fifteen.

Most conventional processes for casting acrylic sheet having a thicknessof 0.5 inch or less require a lengthy polymerization time ranging fromabout 12 to more than 24 hours. For articles having a smallest dimensionlarger than 0.5 inch, the casting procedure is also conducted atsuperatmospheric pressure. Extreme care and carefully controlledconditions are required to produce a cast acrylic sheet free frombubbles and voids. Such care is necessitated by the fact that acrylicresins polymerize with the evolution of large amounts of heat eventhough the application of a certain amount of heat is desirable at theonset and at the end of the polymerization to reduce the total curingtime. In a casting polymerization of acrylic sheet, the polymerizationproceeds slowly at first and is accelerated by the application of heat.The monomer is of low viscosity and chain termination and initiation arebalanced. As the polymerization monomer reaches the gel stage, chaintermination is diminished and the internal temperature rises sharply,thereby accelerating the polymerization even more and causing theevolution of even more heat. If the exotherm is not controlled, the heatbuildup can cause the monomer to boil, thus producing a sheet full ofbubbles and disfigurations, or even worse, the reaction may reach thepoint of explosive violence resulting in damage to the molds and otherequipment. If the exotherm is controlled and the system is brought tosubstantial completion without damage to the casting, heat is againapplied to polymerize the remaining 3 or 4% residual monomer. A typicalprocedure for casting a or 75 inch sheet of polymethyl methacrylatecomprises adding 0.5% benzoyl peroxide to the uninhibited monomer andheating the mixture with agitation to about 90 C. for eight to tenminutes, followed by rapid cooling to room Patented May 6, 1969temperature. The prepolymer so formed can then be treated withplasticizers, fillers, dyes, pigments, stabilizers and the like, afterwhich time the prepolymer is deaerated and either refrigerated or usedimmediately. When ready for casting, a flat sheet mold is filled withthe prepolymer syrup and placed in an oven at 42 C. for 12 to 18 hours,after which time the sheet is heated to to 98 C. over a one hour periodand held at this temperature for an additional 30 minutes. Despite theproduction costs connected with such a manufacturing process, the demandfor east acrylic sheet has continued to increase. The clarity,brilliance, and almost gem-like quality of cast acrylics have done muchto convince the public that plastics are not cheap substitutes but newmaterials with a new scope of uses.

The acrylics are also useful in a variety of applications utilizing someof their physical and mechanical properties other than clarity such asweather resistance, good tensile properties and impact strength. Someapplications for translucent or opaque acrylics include outdooradvertising displays, exterior and interior wall cladding, roomdividers, shower enclosures and doors.

In addition to polymerization casting, injection molding and extrusioncan also be used to prepare acrylic sheet. A comparison of propertiesshows that cast acrylic is a better product. Cast sheet is harder thanextruded sheet, has a higher tensile strength, lower elongation, betterheat distortion properties and better machining characteristics.Extruded sheet has a price advantage, however.

Recently, an accelerated catalyst system has been developed whichpermits a reduction in total casting time from about 24 hours or more toabout two hours or less. This system utilizes an accelerator comprisinga boron compound of the formula BR where each R can be a hydrogen,hydrocarbon, hydrocarbonoxy, halogen, or --OBR group. The boron compoundis complexed with a weak base having an ionization constant in the rangeof 10* to 10* to form an accelerator of the desired reactivity with theperoxygen free radical catalyst. By careful temperature control in somemedium such as a water bath to insure good heat transfer, a flawlesssheet inch thick can be cast in 45 minutes to an hour using theaccelerated catalyst system just described. A subsequent one hour cureat an elevated temperature completes the polymerization. The enormousreduction in polymerization time is sufiicient to place cast acrylics onan economically competitive basis with molded and extruded acrylics.

Another recent development in the area of cast acrylic technologycomprises the coupling of acrylic resins to inorganic materials throughdifunctional organosilicon compounds having at least one functionalgroup for reaction with the surface of the inorganic and at least onefunctional group for interpolymerization into the acrylic polymer chain.Such a process permits the fabrication of acrylic sheet having increasedtensile and flexural strengths and moduli with little or no loss inimpact strength, albeit a reduction from crystal clarity to translucenceor opacity.

Although the accelerator system discussed above represents a significantadvance in the area of acrylic polymerization, even further reductionsin polymerization time would constitute another improvement. If,simultaneously with such an improvement, a process could be employedwhich would produce a cast acrylic sheet of exceptionally goodmechanical properties, the advantages would be obvious-the fabricationof a mechanically superior cast acrylic sheet in a matter of minutes.Providing a process capable of achieving the above improvementsconstitutes the principal objects of the present invention. Additionalobjects, benefits and advantages will become apparent in view of thefollowing detailed description.

The instant invention is directed to a process for casting acrylic sheetcomprising polymerizing an alkyl methacrylate monomer in the presence ofa free radical catalyst whose decomposition is accelerated by acomplexed boron compound of the formula Z-BR where each R can be ahydrogen, hydrocarbon, hydrocarbonoxy, halogen, or OBR group and Z is aweakly basic complexing agent having an ionization constant in the rangeof about 10* to and in the presence of at least 33% by weight inorganicmaterial, said material being sufiiciently dispersed and distributedthroughout the monomer to serve as an effective heat sink for theexothermic heat of polymerization.

The alkyl methacrylate monomers useful herein in clude methylmethacrylate, ethyl methacrylate, n-propyl methacrylate, isopropylmethacrylate, and the isomeric butyl methacrylates. Monomer mixtures canalso be employed. A preferred mixture consists of methyl methacrylateand one or more alkyl acrylates or alkyl methacrylates, e.g., ethylacrylate, propyl acrylate, 2-ethyl hexyl acrylate, butyl methacrylateand lauryl methacrylate. Polymeric network structures, in distinction togenerally linear structures, can be obtained by polymerizing an alkylmethacrylate with a polyfunctional methacrylate such as ethylene glycoldimethacrylate, propylene glycol dimethacrylate, butylene glycoldimethacrylate, polyethylene glycol dimethacrylate andtrimethylolpropane trimethacrylate. Thus, the term alkyl methacrylatepolymer as used herein, is intended to include alkyl methacrylatehomopolymers and alkyl methacrylate copolymers of alkyl methacrylateswith other alkyl methacrylates and/or alkyl acrylates. Alkylmethacrylate polymers also encompass the copolymers of an alkylmethacrylate with other monomers copolymerizable therewith, for examplestyrene, a-methyl styrene and other substituted styrenes such as thering-substituted methyl styrenes, biallyl, acrylonitrile, maleicanhydride, 2-hydroxy alkyl methacrylates and methacrylonitrile.

The alkyl methacrylate polymers useful in the preparation of these novelcompositions can be linear or crosslinked. Crosslinking provides someimprovement in physical properties, particularly heat distortiontemperature, but the linear polymers are also definitely included withinthe scope of this invention. The maximum amount of tolerablecrosslinking in the polymer depends upon the proposed use of thefinished composition. Increased crosslinking produces compositions withhigher heat distortion temperature, but somewhat lower impact strentghand fiexural strength. Consequently, control of crosslinking provides avariable which enables one to tailor the polymer to produce acomposition of the desired properties. A suitable amount of crosslinkingis that which will provide a polymer with an effective molecular weightaround 20,000 or more, preferably 30,000 or more. Therefore a linearalkyl methacrylate polymer with a molecular weight around 20,000 or moremay not need to be crosslinked whereas a lower molecular weight polymer,e.g. a polymer with a molecular weight of 5,000 or less, would be betterutilized in the practice of this invention if it were crosslinked.Suitable crosslinking agents are well known in the art and can be usedhere in the conventional manner. Crosslinking can be achieved throughthe coupler by hydrolysis of silanol groups to form siloxane linkages,i.e.

and by the use of polyfunctional monomers as described above. Similarly,the term alkyl methacrylate refers to the monomer alone as well asmixtures of alkyl methacrylates with other monomers such as set forthabove.

Inorganic materials suitable for use as fillers or reinforcing agentsare those materials which are substantially insoluble in water, i.e.less soluble than 0.15 gram per liter. Such materials can be selectedfrom a variety of minerals, primarily metals, metal oxides, metal salts$119 1 as me al aluminates and metal silicates, other siliceousmaterials, and mixtures thereof. Generally, those materials which haveor can acquire an alkaline surface upon treatment with a base are bestsuited for the reinforcement of polymeric compositions. Since metalsilicates and siliceous materials usually have or can readily acquirethe desired alkaline surface, a preferred mixture for use in thisinvention is one which contains a major amount, i.e. more than 50% byweight, of metal silicates or siliceous materials. Materials with suchcharacteristics are preferred because of the ease with which they can becoupled to the polymer. However, other substances such as alumina 'whichare coupled to an alkyl methacrylate polymer by the use of higher levelsof coupling agents, can be used as reinforcing components either singlyor preferably combined with other minerals which are more susceptible tocoupling, and more preferably combined in minor amounts, i.e.percentages of less than 50% of the total reinforcing material. Anexample of such a material useful as a reinforcing agent, with whichalumina can be mixed, is feldspar, an igneous crystalline mineralcontaining about 67% SiO about 20% A1 0 and about 13% alkali metal andalkaline earth metal oxides. Feldspar is one of the preferredreinforcing agents of this invention and a feldspar-alumina mixture isalso useful. Other materials particularly preferred as reinforcingagents are those materials with an alkaline surface such aswollastonite, which is a calcium metal silicate; asbestos, such aschrysotile, a hydrated magnesium silicate; crocidolite; and othercalcium magnesium silicates. Other useful reinforcing agents include:quartz and other forms of silica, such as silica gel, ground glass,glass fibers, cristobalite, etc. metals such as aluminum, tin, lead,magnesium, calcium, strontium, barium, titanium, zirconium, vanadium,chromium, manganese, iron, cobalt, nickel, copper, and zinc; metaloxides such as oxides of aluminum, tin, lead, magnesium, calcium,strontium, barium, titanium, zirconium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, and zinc; heavy metal phosphates, sulfidesand sulfates; and minerals and mineral salts such as spodumene, mullite,mica, montmorillonite, kaolinite, bentonite, hectorite, beidellite,attapulgite, graphite, chrysolite, garnet, saponite and hercynite. Theterm inorganic material" or simply inorganic used in this disclosurerefers to materials such as exemplified above. Particularly preferredare those inorganic siliceous materials which have or can acquire analkaline surface upon treatment with a base and which have a 3-dimensional crystal structure as opposed to a 2-dimensional or planarcrystal configuration. These siliceous materials are also characterizedby a somewhat refractory nature with a melting point above about 800 0.,a Mohs hardness of at least 4, and a water solubility of less than 0.1gram per liter. Examples of preferred siliceous materials includeminerals such as feldspar, quartz, wollastonite, mullite, wyanite,chrysolite, cristobalite, crocidolite, fibrous aluminum silicate havingthe formula Al- SiO spo-dumene and garnet. These minerals are especiallydesirable for use in the reinforcement of polyalkyl methacrylatecompositions for a number of reasons. For mstance, they provide acomposition with better abrasion resistance, fiexural strength andmodulus, tensile strength and modulus, impact resistance, resistance toheat distortion and resistance to thermal expansion than do conventionalclay fillers and inorganic pigments such as whiting. Further, theyprovide higher loading levels than can be achieved with glass fibers, animportant economic consideration. In addition, these highly loadedmonomer slurnes can be directly cast into a final polymerized formthereby eliminating several processing steps necessary withglass-fiber-reinforced compositions. The amount of filler or reinforcingagent to be used 1n the preparation of the polymeric composition canvary over a Wide range with the maximum content being limlted primarilyby the ability of the polymer to bind the reinforcing medium into acohesive mass. Techniques subsequently described herein have enabled meto prepare polymeric compositions containing as much as 85 or 90% byweight inorganic. The lower range of inorganic concentration is limitedto about 33% by weight. Although some benefits of shortenedpolymerization time can be attained by using less than 33% inorganic orby using a fibrous mat or other shape or size of inorganic such ascoarse A inch aggregate, the improvement is not significant until theinorganic acting as a heat sink acquires the limitations of size, shapeand quantity imposed hereinabove and below. A preferable lower limit forthe inorganic is 40% by weight of the total composition. Suitable valuesfor inorganic concentration in the finished composition range from about40 to 90% and more preferably from about 50 to 90% by weight of thetotal composition. Objects which are not to be subsequently reworked canbe prepared with higher levels of reinforcing agent.

Inorganic shape, size and size distribution are importantconsiderations. Generally, the greatest improvements in mechanicalproperties are achieved by the use of fibrous inorganics such as glassfibers. For the inorganic to function as an effective heat sing,however, in the particular methacrylate polymerization under discussionwhen only 33% by weight inorganic is employed, it is necessary for theinorganic to be of such a shape and size to permit thorough dispersion.Particles which pass through an 18 mesh sieve of the US. sieve series(US. Bureau of Standards, Standard Screen Series, 1919) are capable ofsufiiciently good dispersion that a methacrylate slurry containing only33% inorganic can be polymerized rapidly and smoothly. If 50 or 60 or70% inorganic is used, the inorganic can be more fibrous in nature, of alarger size, or both. As a general rule, the upper limit on the size ofinorganic is limited to the smallest dimension of the cast article. Inthe case of inch acrylic sheet, this would be A inch. Usually, most ofthe inorganic is such that it will pass an 18 mesh sieve (1000,14).Particles as small as 100 or 200 millimicrons can also be used.

Particle size distribution is a variable which permits good packing ofinorganic to achieve high loadings and good heat sink characteristics.More descriptive of suitable particles than limits on particle size is aspecification of particle size distribution. A suitable wide particlesize distribution is as follows:

A narrower distribution also suitable for use in this invention is.

Percent 62 or less (230 mesh) 100 44,11. or less (325 mesh) 90 11p. orless 50 8a or less 10 A relatively coarse mixture useful in thisinvention has the following particle size distribution:

Percent 250,14 or less (60 mesh) 100 149,14 or less (100 mesh) 90 105,14or less (140 mesh) 50 44,11. or less (325 mesh) 10 A suitable finelydivided mixture has the following particle size distribution:

Percent 44 or less (325 mesh) 100 10 or less 90 2 or less 50 0.5 or less10 These figures regarding particle size distribution should not beconstrued as limiting since both wider and narrower ranges ofdistribution will also be useful as well as both coarser and finercompositions. Rather these figures are intended as representativeillustrations of inorganic compositions suitable for use in preparingthe reinforced polymeric compositions. As an example of the variety ofparticle sizes which can be used in the subject reinforced polymericcompositions, large aggregate an inch or more in diameter can also beincorporated into the polymer matrix for special effects. Examplesinclude ground glass, roofing granules, quartz chips, etc.

Although high loadings and good heat sink characteristics dictate that agranular or acicular inorganic be used, a need for exceptionalmechanical properties may require that a quantity of fibrous inorganicbe used. The most common fibrous reinforcing agent used is fibrous glassparticles. These fibers are most easily incorporated into the polymericcomposition when chopped into strands approximately 0.1 to 3 inches inlength, and then either added to a prepolymer-coupler mixture asdiscrete particles or formed into a mat upon which the prepolymer ispoured prior to polymerization. These methods of incorporation of glassfibers are known in the art and are mentioned here to demonstrate thatthe granularly reinforced polymers of this invention can be additionallyreinforced by incorporation of fibrous materials according to techniquesknown in the art or according to the procedure described herein asapplicable to granular inorganics.

After optimum particle size distribution of the reinforcing agent isselected for a particular polymer system, it can be appreciated that anupper limit of inorganic can be reached at which point the compositionbecomes too viscous to be poured into a mold. The viscosity ofmonomer-inorganic slurries can be reduced by surfactants. Loweredviscosity permits the formation of a finer, smoother finish on the finalproduct. Occasionally a finished composition with a high inorganiccontent e.g. greater than 70%, may have a granular or coarse texture andmay even contain voids or open spaces due to the inability of theviscous mixture to flow together completely prior to polymerization. Theaddition of a surfaceactive agent eliminates this problem and produces asmooth, attractive finish on highly loaded compositions. If a smoothfinish is not a necessary feature for certain applications, then adecrease in viscosity permits incorporation of large amounts ofinorganic into the monomer feed. Anionic, cationic, or nonionic surfaceactive agents can be used to reduce the slurry viscosity and materialssuch as zinc stearate, long alkyl chain trimethylammonium halides, andalkylene oxide condensates of long carbon chain compounds have been usedsuccessfully.

As catalysts for inducing the polymerization reaction there may be usedany compounds which will generate free radicals under the reactionconditions, although the hydroperoxy compounds are preferred. Specificclasses of compounds which can be used include peroxides, such asdi-acetyl peroxide, acetyl benzoyl peroxide, dipropionyl peroxide,dilauryoyl peroxide, benzoyl peroxide, dimethyl peroxide, diethylperoxide, dipropyl peroxide, tetralin peroxide, cyclohexane peroxide,acetone peroxide; hydroperoxides such as cyclohexyl hydroperoxide,cumene hydroperoxide, t-butyl hydroperoxide, methyl cyclohexylhydroperoxide, hydrazine derivatives, such as hydrazine hydrochloride,hydrazine sulfate, dibenzoylhydrazine, diacetylhydrazine,trimethylhydrazinium iodide; amine oxides, such as, pyridine oxide,trimethylamine oxide, dimethylaniline oxide; alkali metal and ammoniumpersulfates, perborates, and percarbonates; compounds containing thegroup 'C=N- and derived from ketaldones, Le. a ketone or aldehyde, suchas the azines (containing the group C=NN=C e.g., benzalazine,heptaldazine and diphenylketazine; oximes (containing the group C=NOH)such as d-camphor oxime, acetone oxime, alphabenzil dioxime,butyraldoxime, alpha-benzoin oxime, oxime, dimethylglyoxime; hydrazones(containing the group C=N-N such as benzaldehyde phenylhydrazone,phenylhydrazones of cyclohexanone, cyclopentanone; semicarbazones(containing the group such as semicarbazones of acetone, methyl ethylketone, diethyl ketone biacetyl, cyclopentanone, cylohexanone,acetophenone, propiophenone, camphor and benzophenone; Schiffs bases(containing the group C=N) such as benzalaniline, benzal-p-toluidine,benzal-o-toluidine, benzaldehyde derivatives of methylamine, ethylamineand heptylamine, anils and analogous compounds of other amines, such asacetaldehyde anil, iso'butyraldehyde anil, heptaldehyde anil, etc.;oxygen; and the reaction products of organometallics such as cadmiumalkyls, zinc alkyls, tetraethyl lead, aluminum alkyls, etc. with oxygen.

These catalysts are generally used in amounts from about 0.001% to 0.5%by Weight based on the total reactants. While it is generally notnecessary, for attaining extremely high rates of reaction or for otherspecial purposes, even higher amounts of catalysts may be used; forexample, amounts ranging up to as high as 1% or even 5% as an upperlimit can be employed.

Compounds used as activators include the boron hydrides (boranes) andsubstituted boranes such as borane, diborane, triborane, tetraborane,trimethylborane, triethylborane, tripropylborane, trihexylborane,trioctylborane, tridecylborane, tri-tridecylborane, tricyclohexylborane,triphenylborane, tribenzylborane, triphenethylborane,tri-monomethylbenzylborane, and tritolylborane. Preferred aretrialkylboranes where each alkyl group has from 1 to about 14 carbonatoms.

The boron compounds are complexed with a basic complexing agent havingan ionization constant from about l to about preferably from 10 to l0Particularly preferred are amino compounds having an ionization constantbetween 10"" and 10 one notable example being pyridine. Other suitableamines which can be used include methylamine, di-methylamine,trimethylamine, dimethylbutyl amine, n-octylarnine, the picolines,aniline, dimethylaniline, the toluidines, triethylenediamine andmixtures of several different amines. The mole ratio of amine to boroncompound is within the range of 0.1:2 to about 10:1, and is preferablywithin the range of 0.5:1 to 2:1.

The catalyst system, a trialkylborane-complexing agent with a preferredhydroperoxide compound, permits a rapid polymerization reaction to highconversion without the risks of a runaway-type reaction. Although aminesare preferred as complexing agents for the trialkylborane, othercompounds can also be used for this purpose such as tetrahydrofuran,triphenylphosphine, beryllium hydroxide, strychnine, codeine, cocaine,novacain, toluidine and nicotine.

As the subsequent examples will show, a filled alkyl methacrylate sheet7 inch thick can be cast in less than ten minutes, representingapproximately a twelve-fold reduction in casting time by comparison to asimilarly prepared unifilled sheet. Further, the accelerator andcatalyst can be modified to provide a smooth, fast, trouble-free, roomtemperature polymerization.

The mechanical properties of the filled acrylic sheets are as expected.The sheets are more rigid (higher modulus) but also weaker (lowertensile and fiexural strengths) and more brittle (lower impactresistance). As a result, their use is restricted. The mechanicalproperties of the filled acrylic sheets can be upgraded considerablyeven to exceed the properties of an unfilled sheet by converting theinorganic filler to a reinforcing agent through use of a coupler.

An essential material in the preparation of reinforced polymericcompositions is the coupling agent which binds the inorganic to thepolymer. A coupling agent can be characterized by its functional groupswherein one group is capable of reaction with the monomer duringpolymerization and at least one group is capable of reaction with theinorganic. Preferred coupling agent contain an organic group having aterminal carbon to carbon double bond and at least one hydrolyzablegroup attached to silicon atom. The inorganic and coupler are joined bycombining them in the absence or presence of water, alcohol, doxane,etc. Presumably, the hydrolyzable group of the coupler reacts with thehydrogen atoms of appended hydroxyl groups attached to the surface ofinorganic materials having an alkaline surface. Theoretically, thesehydroxyl groups are present on the surface of, or can be developed uponthe surface of, most metallic and siliceous substances, therebyproviding a site available for reaction with a hydrolyzable silanegroup. This theory of availability of hydroxyl groups on an inorganicsurface may explain why many silicon-containing minerals are preferredreinforcing agents since the reaction of the hydrolyzable silane groupsof the coupler with the silanol groups, i.e.

b:iOH of the reinforcing agent produces the very stable siloxanelinkage,

Regardless of any theoretical explanation advanced herein, to which I donot intend to be bound, the oxysilane group is attached to the inorganicby contacting the two components. The composition is preferably but notnecessarily subsequently dried. A bond between the inorganic and coupleris thus obtained. This reaction of inorganic and coupler may be carriedout separately, and the dried inorganic-coupler adduct subsequentlyadded to the monomer, or the reaction may be carried out in the presenceof the monomer and the whole mixture dried to remove volatile reactionproducts and solvent, if used. Preferably, heat is applied to acoupler-inorganic mixture to increase the extent of bonding.

Preferred silane coupling agents are characterized by the formula whereZ is a radical interpolymerizable with a methacrylate monomer orreactive with a polyalkyl methacrylate polymer, examples being vinyl,allyl, acryloxy methacryloxy, and other radicals containing ethylenicunsaturation, Y is a hydrocarbyl radical, X is a radical capable ofreaction with the surface of an inorganic, examples being halogen,alkoxy, cycloalkoxy, aryloxy, alkoxycarbonyl, aryloxycarbonyl, alkylcarboxylate, aryl carboxylate, and hydroxyl radicals, n is an integerfrom 1 to about 20, a is an integer from 1 to 3, b is an integer from 0to 2, c is an integer from 1 to 3, and the sum of a+b+c equals 4.Particularly preferred are coupling agents of the above formula wherethe integer a is 3, b is 0, and c is 1, where X is an alkoxy radical,and Z is a methacryloxy group, e.g.

The function of the Z group and X group have already been discussed. Thealkylene group in the formula above, (CH serves as a bridge between thepolymer-reactive group and the silane group of a coupler. The alkylenebridge is usually present in a coupling agent because of the additionalstability it contributes to the coupling agent. The Y group can be anyhydrocarbyl group; the function of the Y group can be to modify theextent of the polymer-inorganic bond, to regulate viscosity of themonomer slurry, or it need not serve any function at all in thepolymeric composition. Its presence may be due to a necessity ordesirability to use a hydrocarbyl-substituted silane reactant in thesynthesis of a silane coupler. Examples of suggested couplers includevinyl triet-hoxysilane, vinyl methyldichlorosilane, di-(3-methacryloxypropyl) dipropoxysilane, and 6-acryloxyhexyltricyclohexoysilane.

In addition to silicon-based couplers, phosphorus-based couplerscomprise another class of reinforcing agents. These compounds,containing functional groups corresponding to the X, Y and Z, groups ofthe above formula, are adequately exemplified in R. E. Millers copendingapplication Ser. No. 333,630, filed Dec. 26, 1963, now Patent No.3,344,107. Other compounds useful as coupling agents include thecoordinated chromium complexes which contain at least onepolymer-reactive radical and at least one inorganic-reactive radicalcorresponding to the Z and X groups of the formula above. Examplesinclude methacryloxychromic chloride, acryloxy chromic chloride,crotonyloxy chromic chloride, sorbyloxy chromic chloride,3,4-epoxybutylchromic chloride, and methacryloxy chromic hydroxide.Other difunctional compounds useful as couplers include sodium salt ofmethacrylic acid, allyl chloride, methyl ester of 3,4-epoxybutanoic acidand 1-hexenol-6.

The amount of coupler with which the reinforcing agent is treated isrelatively small. As little as one gram of coupling agent per 1000 gramsof reinforcing agent produces a polymeric composition with physicalproperties vastly superior to those of a polymeric compositioncontaining an untreated filler. Generally, quantities of coupler in therange of 2.0 to 20.0 grams per 1000 grams of reinforcing agent have beenfound most satisfactory although quantities in excess of that range mayalso be used with some detriment to the properties of the finishedproduct.

The actual steps in the polymerization can be carried out in a number ofways. For instance, the inorganic and monomer can be mixed together inthe presence of atmospheric oxygen which acts as a polymerizationinhibitor. An organic hydroperoxide or other inefiicient methacrylatepolymerization catalyst can be added to the monomer-inorganic slurryfollowed by the complexed borane accelerator, after which addition thecatalyzed slurry is cast into the molds. The advantage of such aprocedure is that the molecular oxygen which acts as an inhibitor beforethe accelerator is added, acts as a catalyst after addition of theborane. Hence, the system operates to best advantage without thenecessity for excluding or removing oxygen at some stage of thereaction. Alternatively, the accelerator can be added to an oxygen-free,uncatalyzed inorganic-monomer slurry followed by addition of thecatalyst. Or both accelerator and initiator can be added to anoxygen-free system at C. and then cast into a mold at some highertemperature. If a coupling agent is used, the coupler can be combinedwith the inorganic prior to or subsequent to addition to the monomer.Substantial coupler-inorganic reaction is aided by application of heatin the range of 90 to 100 C. When the alkyl methacrylate monomer is usedas a dispersing solvent, a satisfactory technique for achieving goodcouplerinorganic reaction comprises adding the coupler to the monomer,adding the inorganic to the mixture, stirring thoroughly and heating to100 C., cooling the resultant slurry to 0 to 25 0., adding initiator andaccelerator, and casting into a mold.

Another component which can be added to the monomer slurry to modify theproperties of the cast methacrylate article is a rubbery polymer. Therubber can contribute to the impact strength of the finishedcomposition. The rubbery polymer component can be used in quantitiesranging up to about more preferably from about 1% to about 10%, byweight of the alkyl methacrylate polymer. Higher rubber contents are ofcourse included within the scope of this invention, especially if therubber selected is a partially degraded, low molecular weight rubber oflow viscosity. Reinforced polyalkyl methacrylates having up to about 10%dispersed rubber based on the alkyl methacrylate can be readily preparedusing techniques described in the subsequent examples. Handlingdifiiculties are experienced when the rubber content is increased beyond10 or 11%. Other techniques such as a pressurized injection into themold are of course available and permit the polymerization of castshapes of reinforced polyalkyl methacrylate having 20% or more dispersedrubber. The present invention is limited in one preferred aspect,however, to compositions having a maximum of about 15% by weightdispersed rubber based on the alkyl methacrylate. This is because of theunsatisfactory fiexural properties achieved at higher rubberconcentrations. A maximum rubber concentration of 10% is particularlypreferred because of the ease of casting and molding combined with thevery extensive and satisfactory range of mechanical properties which canbe achieved in reinforced methacrylates having from 1 to 10% dispersedrubber.

For convenience in preparing the reinforced compositions, selection of arubbery polymer that is soluble in the alkyl methacrylate monomer systemis preferred, although other rubbers not completely soluble can be usedwith some sacrifice in product uniformity. Suitable rubbery polymersinclude the polybutadiene rubbers, polyisoprene rubbers,styrene/butadiene rubber, natural rubber, acrylonitrile/butadienerubber, butadiene/vinyl pyridine rubber, butadiene/styrene/vinylpyridine rubber, polychloroprene, isobutylene/isoprene rubber,ethylene/vinyl acetate rubber, ethylene/propylene rubber andethylene/propylene/conjugated diene rubber. Preferred are those rubberypolymers named above which contain little or no crosslin'ked gel.

The rubber must be thoroughly dispersed throughout the reinforcedmethacrylate composition. To achieve the maximum benefits of thisinvention, namely optimization of fiexural strength and modulus as wellas impact resistance by comparison to an unreinforced polyalkylmethacrylate, it is necessary that the rubber be interpolymerized intothe methacrylate polymer chain. A simple blend of the polymericcomponents will not yield as satisfactory a combination of mechanicalproperties as will an interpolymer of the rubber and polyalkylmethacrylate. Simple noninterpolymerized reinforced methacrylaterubberblends are nevertheless useful for certain applications where impactstrength is not an essential feature. As an example, 1 to 5% of asaturated acrylic rubber, incapable of substantial interpolymerization,is useful in reinforced polyalkyl methacrylate floor tiles to preventthe yellowing that accompanies use of unsaturated rubbers. Retardationof settling of particulate reinforcement can also be achieved by use ofnoninterpolymerized dispersed rubbers.

In order to illustrate some of the various aspects and advantages of theinvention, representative examples are given herein. It will, of course,be understood that variations can be made in the reactants andconditions of the examples without departing from the invention.

EXAMPLE 1 To 2000 grams of wollastonite isv added 1200 ml. of methanolcontaining 5 grams of Z-methacryloxyethyl trimethoxysilane. A slurry ismixed and placed in a hood to evaporate the methanol. The mineral isthen heated at 210 C. in an oven for 75 minutes, cooled and milled in aball mill. To 335 grams of methylmethacrylate is added 6.7 grams ofbenzoyl peroxide and 782 grams of the treated wollastonite. Afterthorough mixing, the slurry is subjected to a vacuum of approximately 55mm. of mercury for about 5 minutes. The slurry is then cast into a moldpreheated to 65 C. and is maintained at this temperature for 20 hours.The resultant polymeric composition contains 70% by weight wollastoniteor a volume fraction of 0.42.

EXAMPLE 2 A glass reactor was charged with 175.0 g. methyl methacrylateand 408.2 g. of Supersil silica sand of 325 mesh.

1 1 The charge of silica sand gave a calculated volume fraction of 0.43,which is equivalent to 68% by weight of the total composition. To thewell stirred slurry was added 4.38 ml. cumene hydroperoxide followed by11.5 ml. of a solution of triethylborane/pyridine complex in anonylphenol-ethylene oxide condensation product. This catalyst componentwas prepared by adding 115.4 ml. pyridine to a solution of 140.6 g.triethylborane and 341.8 ml. of the nonylphenol-ethylene oxidecondensate (Tergitol NP-27). The reactants were thoroughly mixed for 30seconds and then poured into a plate mold wherein the plates were spacedinch apart by a rubber gasket. The mold was preheated to 40 C. and thepolymerization exotherm, reaching 51 C., was observed after thereactants had been in the mold for about 30 minutes. The mold wasimmediately opened after the exotherm was measured and a smooth glossysolid composition obtained. Samples were cut from this plate forphysical testing (Table I).

EXAMPLE 3 The procedure and charge used in this run were identical tothose of Example 2 with the exception that in the instant example theSupersil silica sand was treated with a coupling agent prior to mixingwith the other reactants. The silica sand, 500 g. was treated with 250ml. methanol containing 1.25 g. 3-methacryloxypropyl trimethoxysilane.The methanol was then evaporated from the well stirred slurry atatmospheric pressure and the treated silica sand finally dried in anoven at 210 C. for 1 hour and fifteen minutes.

The polymerization exotherm was measured at 49 C. 30 minutes after theslurry was transferred to the preheated mold. The mold was then cooledto room temperature, opened and a smooth glossy solid polymercomposition removed and cut with a diamond saw to obtain samples forevaluation (Table I).

EXAMPLE 4 To a quantity of 525 grams of methyl methacrylate is added13.1 ml. of cumene hydroperoxide and 34.5 ml. of a solution of thetriethyl borane-pyridine complex dissolved in the nonylphenolethyleneoxide condensation product. After mixing the catalyst, accelerator andmonomer for 30 seconds, the catalyzed monomer is cast into a inch thicksheet mold cooled to 20 C. in a water bath. The peak exotherm occursabout 2 hours after casting and reaches about 95 to 100 C. if thetemperature is closely regulated. The sample is allowed to cool to 90 C.and held at this temperature for an additional thirty minutes.Properties of the finished article, reported in Table I, are comparableto the properties of a conventionally cast polymethyl methacrylatesheet.

EXAMPLE 5 A comparison of the products prepared in Examples 1, 2, 3 and4 is made in Table I.

It can be seen that the product of Example 2, which does not contain acoupling agent, does not have the surprising properties of fiexuralstrength possessed by the prodno of Example 3. The reinforcedcomposition prepared in Example 3 exhibits more than 210% increase infiexural strength over the product of Example 2 prepared without thecoupling agent. Flexural modulus is also increased. The flexuralstrength and modulus are determined by ASTM D790. Regardless of whetheror not a coupler is used, the complexed borane accelerator results in adramatic reduction in polymerization time.

Example 1 sets forth a conventional procedure for casting an acrylicsheet using an unaccelerated peroxide catalyst. Example 4 demonstratesthe approximately 10 fold reduction in time achieved by the use of thecomplexed borane accelerator. Examples 2 and 3 demonstrate the evenfurther improvement achieved by the addition of an inorganic phase as aheat sink, and as an agent to improve the thermal conductivity of thecasting. Comparison of the mechanical properties of the four samplesshows that use of a coupler is advisable if mechanically strong acrylicsheet is to be prepared in a very short casting cycle such as 30 minutesor less.

EXAMPLE 6 Examples 6 and 7 are provided to demonstrate the changes inmechanical properties of reinforced polymers that are made by methodsused to couple the particulate mineral to the polymer.

In this run a glass reactor is charged with 350g. methyl methacrylate,4.0 g. trimethylolpropane trimethacrylate and 700 g. wollastonite thathad been treated with 3-trimethoxysilylpropyl methacrylate in methanolsolution (5.0 g. of the coupling agent per 2000 g. of wollastonite). Themineral-coupling agent had been dried in an oven at 210 C. for 75minutes, cooled and ground in a ball mill prior to use. These reactantsare thoroughly stirred in the reactor and 8.75 ml. cumene hydroperoxideadded followed by the addition of 24.5 ml. triethylborane/pyridinecomplex in the ethylene oxide-nonylphenol condensate as described inExample 2. Thorough mixing is continued for 30 seconds and the reactionmixture then poured into a simple polished plate mold at 40 C. Theplates of the mold are separated inch by the use of rubber gaskets.After 13 minutes polymerization time within the mold, the maximumreaction exotherm occurs, reaching 55 C. The mold is immediately cooledand the sample removed from the plates. The solid polymeric sheet is cutinto two pieces. One piece is further divided to obtain samples forphysical testing and the other piece post cured for 17 hours in an ovenat C. Evaluation data is reported in Table II.

EXAMPLE 7 The weight of reactants used in this run is generallyequivalent to the weight used in Example 6 but the general procedure ismodified. A glass reactor is charged with 350 g. methyl methacrylate and8.4 g. trimethylolpropane trimethacrylate. The wollastonite used in thispreparation had been ground in a ball mill and dried in an oven at 90 C.for 16 hours and then cooled. The wollastonite, 700 g., is added inportions to the reactor along with 3.75 ml. cumene hydroperoxide and1.68 ml. 3-trimethoxysilylpropyl methacrylate. The reactants arethoroughly agitated in an atmosphere of nitrogen and then 24.5 ml. ofthe triethylborane/pyridine catalyst is added, as used in Example 6. Thematerials are thoroughly mixed for 30 seconds and then poured into aplate mold preheated to 40 C. The maximum reaction temperature reaches82 C. 17 minutes after the material is transferred to the mold. The moldis cooled, the solid glossy product removed from the mold and cut into 2pieces, 1 of which is subjected to a post cure in an oven at 90 C. for17 hours. Thereafter samples are cut from both sections for evaluationfor physical properties (Table II).

EXAMPLE 8 In this run the reactor'is charged with 350 g. methylmethacrylate, 8.4 g. trimethylolpropane trimethacrylate, 1.68 ml.3-trimethoxysilylpropyl methacrylate and 700 g. wollastonite that hadbeen ground in a ball mill. These reactants are thoroughly mixed andthen heated to C. under refluxing conditions. A vacuum is graduallyapplied to the reactor to slowly distill off 15 ml. of liquid. Thereactants are then cooled to room temperature and an addition of 15 ml.methyl methacrylate made. The

13 reactants are stirred in an atmosphere of nitrogen as 8.75 ml. cumenehydroperoxide is added followed by 24.5 ml. triethylborane/pyridinecatalyst as previously described. The mixture is stirred for anadditional 30 seconds and then rapidly poured into a plate moldpreviously heated to 40 C. The peak reaction exotherm occurs 17 minutesafter trans-fer of the material to the mold and was noted at 84 C. Themold is then cooled to room temperature and the composition removed anddivided into two equal sections. One section is post cured for 17 hoursat 90 C. in an oven and then cooled. Thereafter, both sections are cutto prepare samples for physical property evaluation (Table II). Thisexample also demonstrates the feasibility of in situ reaction of couplerand inorganic.

EXAMPLE 9 Physical properties of the product described in Examples 6 to8 are summarized in the following Table II. It can be seen that a postcuring step improves the physical property of each of the samplesevaluated.

TABLE II Flexural Corrected Strength impact strength Post cure (p.s.i.)(it. lb/id. notch) Example 6 15, 500 0.25 16, 000 0. 29 Example 7 9, 8000. 31 10, 600 0.32 Example 8 16, 300 0. 31 17, 000 0.31

The foregoing data indicate that hydrolyzing conditions are required toobtain a chemical bond between the mineral and the coupling agent. Thusin Example 6 and Example 8 water was present, absorbed on thewallastonite, and occurred in a sufficient quantity to hydrolyze thecoupling agent. On the other hand, in Example 7 the water was driven offthe surface of the mineral and hydrolysis of the coupling agent wasprevented. Thus there was not a good chemical bond between thewallastonite and the coupling agent so that the properties of thefinished composition were not nearly as good as those obtained by theprocedures of Example 6 and Example 8.

EXAMPLE 10 To 285 grams of methylmethacrylate is added 15 grams of astyrene/butadiene rubbery copolymer (FRS-182). After solution of thecomponents, 7.5 ml. of cumene hydroperoxide and 600 grams ofwollastonite treated according to the procedure described in Example 1are added. To the resultant slurry is added 28.5 ml. of a solution of atriethylborane/pyridine complex in a nonylphenol-ethylene oxidecondensation product. (Tergitol NP-27). This complex is prepared byadding 140 grams of triethyl borane to a solution of 115 ml. of pyridineand 341 ml. of the nonylphenol-ethylene oxide condensate. After thoroughmixing, the monomer slurry is poured into a mold maintained at roomtemperature. After about an hour, the temperature of the polymerizingmixture rises to a peak of about 50 C. Upon cooling to room temperaturethe resultant polymeric composition is removed. Onehalf of thecomposition is out to prepare samples for evaluation; the second half issubjected to a post cure in an oven for 3 hours at 90 C. and then cut toprepare samples for evaluation. Total elapsed polymerization time isabout 75 minutes at room temperature (25 0.).

EXAMPLE 11 To 1280 grams of methylmethacrylate is added 64 grams of astyrene/butadiene rubbery copolymer (FRS-1006). After solution ofcomponents, 239- grams of wollastonite treated as described in Example1, 31 grams of trimethylolpropane trimethacrylate and 16 ml. of cumenehydroperoxide are added with stirring. After thorough mixing andapplication of a vacuum to remove entrapped air, 42 ml. of thetriethylborane pyridine complex described in Example 10 is added.Stirring is continued for 30 seconds and the reactants then poured intoa simple mold maintained at room temperature. After 1 hour thepolymerized material is removed from the mold. The resultant polymericcomposition contains 4.8% by weight rubbery copolymer and 63% by weightreinforcing agent.

EXAMPLE 12 TABLE III Flexural Flexural Izod Total poly- Polymericstrength, modulus, impact, merization composition (p.l.i p.s.i. it.lb./in. time 10 12,200 1. 1 49 (.2 Post cured 11, 1. 1 55 35) 75 min. (rt l1 15, 600 1. 6 31 10) 60 min. (r t) The above examples demonstrate aroom temperaturepolymerization of an acrylic sheet requiring a totalelapsed time of less than two hours. It should be noted that the moldswere neither heated or cooled externally at any time during the castingcycle.

EXAMPLE 13 To 335 g. of methyl methacrylate is added 23.5 g. of astyrene/butadiene rubbery copolymer (FRS1006), 6.7 g. of acrylonitrile,2.3 ml. of cumene hydroperoxide and 622 g. of wollastonite treated asdescribed in Example 1 except that 3-(trimethoxysilyl)propylmethacrylate is used as a coupling agent. After thorough mixing andapplication of a vacuum, the slurry is charged with 6 ml. of thetriethylborane/pyridine complex described in Example 8. The slurry isstirred for 30 seconds and then poured into a mold preheated to 60 C.After a peak exotherm of 66 C. appearing about 20 minutes after casting,the composition is cooled to room temperature and removed from the mold.The resultant polymeric composition contains 63% by weight reinforcingagent. The polymeric phase contains 2% by weight polymerizedacrylonitrile and 6.6% by weight rubbery copolymer.

EXAMPLE 14- To 295 g. of methyl methacrylate is added 23.5 g. of astyrene/butadiene rubber copolymer (FRS1006), 18 g. of acrylonitrile,2.3 ml. of cumene hydroperoxide and 583.3 g. of wollastonite treated asdescribed in Example 13. After thorough mixing and application of avacuum to remove dissolved and entrapped air, the slurry is charged with6 ml. of the triethylborane/pyridine complex described in Example 8.Following a 30 second agitation, the slurry is cast into a moldpreheated to 60 C. A peak polymerization exotherm occurred at 65 C.about 4 minutes after casting. About 10 minutes after casting, thepolymerized composition is removed from the mold. The resultingpolymeric composition contained 63% by weight reinforcing agent. Thepolymeric phase contained 5.3% polymerized acrylonitrile and 7% byweight rubbery copolymer.

EXAMPLE 15 To g. of methyl methacrylate is added 15 g. of laurylmethacrylate, 10.5 g. of an acrylonitrile rubber copolymer (Hycar 1053),1 ml. of cumene hydroperoxide, 134 g. of wollastonite pretreated with0.25% of trimethoxysilylundecyl methacrylate according to the proceduredescribed in Example 1, and 272 g. of mullite simi- 15 larly treatedwith 0.25% of trimethoxysilylpropyl methacrylate. Following thoroughstirring, the slurry is subjected to a vacuum for about minutes toremove disssolved and entrapped air, after which time 2.7 ml. of thetriethylborane/ pyridine complex described in Example 8 is addded. Theslurry is stirred for 30 seconds and then poured into a mold preheatedto 65 C. The mold temperature rises to 100 C. over a 10 minute periodand is held at this temperature for an additional 10 minutes, afterwhich time the mold is opened and the composition removed. A sample iscut in half and half the sample post cured for 1 hr. at 110 C. Theresulting composition contains 71% by weight reinforcing agent and 6.5%by weight rubbery copolymer based upon the total polymer content. Thenon-rubbery polymeric matrix is a 10/90 lauryl- TABLE V Notched impactPercent Flexural Flexural strength, Polymeric reiniorcestrength,modulus, it. lbs. composition ment p.s.i. p.s.i. in. notch Comparison ofSamples 19 and 20 show the improvement in flexural properties due solelyto the use of ll-trimethoxysilylundencyl methacrylate as a couplerinstead of 3-trimethoxysilylpropyl methacrylate. Sample 18 shows an evenfurther improvement in properties due to the higher content ofreinforcing agent. Samples having 74% reinmethacrylate/methylmethacrylate copolymen forcing agent coupled with3-trimethoxysilylpropyl methacrylate are markedly inferior to any of theabove three EXAMPLE 16 samples, presumably because of the inadequatedispersion The procedure described in Example 15 is followed eX- 0f thenumeral f g p the COmPOSitiOI'I- actly except that 15 g. of monomericethyl acrylate is used l g e lnventlodhas been described in terms of inplace f the lauryl methacry1ate specified embodlments which are setforth in considerable EXAMPLE 17 detail, it should be understood thiswas done for illustrative purposes only, and that the invention is notneces- The following table reports mechanical properties sarily limitedthereto since alternative embodiments and achieved by the use of methylmethacrylate copolymer operating techniques will become apparent tothose skilled systems reinforced according to the practice of thls inthe art in view of this disclosure. For instance, inorganic invention.materials have been discussed exclusively herein because 'lAB LE IVFlexural Flexural Ozod Heat Poly- Iolymeric strength, modulus, impact,distortion, merization composition p.s.i. p.s.i. it. lbs/in. 0. time(min.)

Post cured.- 12, 400 1. 6 14 5,000 0. 84 Post cure 11,800 1. 5 4,1000.85 Post cured-. 10 8,300 1.5 Post cured The above samples arepresented to demonstrate the feasibility of reinforcing methylmethacrylate copolymer systems as well as the feasibility of a 10 minutepolymerization time.

EXAMPLE 18 To 196 grams of methyl methacrylate is added 15 grams of anacrylonitrile rubbery copolymer (Hycar 1053). The mixture is stirreduntil the rubber is dissolved in the methacrylate monomer. To a quantityof 600 grams of wollastonite (200 to 325+ mesh) is added 1.5 grams ofll-trimethoxysilylundecyl methacrylate dissolved in 200 ml. of methanol.The methanol is evaporated from the mineral and the mineral dried at 155C. for 15 minutes. The treated mineral is added to the monomer slurrytogether with 6 ml. of cumene hydroperoxide. To the monomer-mineralslurry, 5 ml. of the triethylborane/pyridine complex in Tergitol NP-27described in Example 8 is added with stirring. After thorough mixing,the slurry is poured into a mold preheated to 60 C. About 5 minutesafter casting, a polymerization exotherm occurs, after which time themold is allowed to cool to room temperature. The finished compositioncontains 74% reinforcing agent. Rubber content based upon the methylmethacrylate is 7%. Mechanical properties are reported in Table V.

EXAMPLE 19 Example 18 is repeated except that the wollastonite contentis adjusted to provide a composition having 70% by weight reinforcingagent. Mechanical properties are reported in Table V.

EXAMPLE 20 Example 19 is repeated except that a comparable quantity of3-trimethoxysilylpropyl methacrylate is used instead of the1l-trimethoxysilylundecyl methacrylate. Mechanical properties arereported in Table V.

of their heat-absorbing characteristics, because of the strength of theinorganic-coupler bond which can be attained and because of the inherentreinforcing capabilities. Materials other than inorganics could be used,however, if one or more of the above or other desirable features can besacrificed. For instance, cellulosic materials such as wood and paper insolid, chip or fiber form have surfaces containing pendant hydroxylgroups which can react with a coupling agent. The bond between couplerand cellulosic material will not be as strong as the couplerinorganicbond previously described nor with the cellulosic material contribute asmuch to the mechanical properties of the polymeric compositions.Nevertheless, several specialty compositions can be manufactured using acellulosic reinforcement. Other materials such as a sintered polyamidemolding powder could also be used. Accordingly, these and othermodifications are contemplated which can be made without departing fromthe spirit of the described invention.

What is claimed is:

1. A process for casting acrylic sheet comprising polymerizing an alkylmethacrylate monomer in the presence of a free radical catalyst Whosedecomposition is accelerated by a complexed boron compound of theformula Z-BR where each R can be hydrogen, halogen or hydrocarbon orhydrocarbonoxy group having from 1 to about 14 carbon atoms or -OBRgroup and Z is a weakly basic complexing agent having an ionizationconstant in the range of about 10- to about 10- and in the presence ofat least 33% by weight inorganic filler material having a watersolubility less than 0.15 gram per liter, said material beingsufiiciently dispersed and distributed throughout the monomer to serveas an effective heat sink for the exothermic heat of polymerization.

2. A process according to claim 1 wherein said alkyl methacrylatemonomer is methyl methacrylate. v

3. A process according to claim 1 wherein said alkyl methacrylatemonomer is a mixture of methyl methacrylate and other acrylic monomers.

4. A process according .to claim 1 wherein said free radical catalyst isa hydroperoxy compound.

5. A process according to claim 1 wherein each R group is an alkyl groupof from 1 to about 14 carbon atoms.

6. A process according to claim '1 wherein said weakly basic complexingagent has an ionization constant of from about to about 10- 7. A processaccording to claim 6 wherein said weakly basic complexing agent is anamine. 7

8. A process according to claim 1 wherein said complexed boron compoundis a triethyl borane-pyridine complex and wherein said alkylmethacrylate is methyl methacrylate.

9. A process according to claim 1 wherein said inorganic material passesthrough an 18-rnesh U.S. sieve..

10. A process according to claim 1 wherein said inorganic fillermaterial from about 40 to about 90% by weight of the monomer-inorganicslurry.

11. A process according to claim 1 wherein a rubbery polymer is added tosaid alkyl methacrylate monomer prior to polymerization.

12. A process according to claim 1 wherein said inorganic fillermaterial is reacted with a coupling agent having at least onehydrolyzable functional group capable of reaction with the surface of aninorganic filler material and at least one functional group containingterminal ethylenic unsaturation which is capable of reaction with saidmonomer during polymerization prior to polymerization of said alkylmethacrylate monomer.

13. A process according to claim 1 wherein said polymerization iscarried out at a temperature below about 70 C.

14. A process for casting acrylic sheet comprising:

(a) mixing together an alkyl methacrylate monomer,

from about 40 to about 90% by weight based on the total mixture of aninorganic filler material which has a water solubility less than 0.15gram per liter and which passes through an 18 mesh U.S. sieve,

a coupling agent having at least one hydrolyzable functional groupcapable of reaction with the surface of an inorganic filler materialand'at least one functional group containing terminal ethylenicunsaturation which is capable of reaction with said monomer duringpolymerization, a rubbery polymer, a hydroperoxy compound, and atrialkyl borane-pyridine complex wherein said alkyl groups have from 1to 14 carbon atoms,

(b) casting the above resultant slurry into ga mold, and

(c) controlling the exothermic heat of polymerization to produce afinished sheet free from bubbles, voids and imperfections.

15. A process according to claim 14 wherein said alkyl methacrylatemonomer is methyl methacrylate and wherein said trialkyl borane istriethyl borone.

16. A process according to claim 14 wherein the polymerization iscarried out in the absence of any external temperature control of thecasting mold or polymerizing monomer.

References Cited UNITED STATES PATENTS 2,742,378 4/1965 Te Grotenhuis260-827 2,952,595 9/1960 Jordan et al. 260-41 2,989,420 11/1958Zdanowski 26031.8 3,079,361 2/1963 Plueddemann 260-41 3,238,186 3/1966Schultz et al. 260--89.5 3,255,168 6/1966 Borsini et a1 260-895 FOREIGNPATENTS 686,760 5/1964 Canada.

OTHER REFERENCES Furukawa et al.: Catalytic Reactivity of OrganometallicCompounds for Olefin Polymerization De Markromolekulare Chemie; BD. 31;159, pages 123-135.

ALLAN LIEBERMA-N, Primary Examiner.

L. T. JACOBS, Assistant Examiner.

US. Cl X.R. 260901 age UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Paced: N 5.442 .851 Dated Mav 6. 1969 Inventot(8) Robert J.McManimie It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 19 "and inorganic" should read an inorganic column 1,line 56 pol merization" should read polymerizing Column 3, line 6"strentgh" should read strength Column 4, line 55 "wyanite" should readkyanite Column 5 line 22 "sing" should read sink Column 6, line 4 "largeshould read larger column 6, lines 73 and 74 'benzoin oxime, oxime,"should read benzoin oxi'me, Column 7, line 2 "cyclopentanone;semicarbazones" should read cyclopentanone, acetophenone, methone,camphor, and benzophenone; semicarbazones column 7, line 58 "unifilled"should read unfilled Column 10, line 6 "methacrylate" should read--methacrylates Column 15, line 25 "(rt-H lb/id. notch)" should read(ft. lb/in. notch) Column 14, line 23 .l.l.)" should read p.s.i. Column15, line 6 "addded" should read added column 15, line 29 "Ozod" shouldread Izod Column 16, line 11 "oxysilylundencyl" should readoxysilylundecyl Column 1?, Claim 10, line23, after "filler materialinsert comprises SI NED AND SEALED MAR 171970 Edward M. Fletcher, Ir.LAttcsting Officer M LER, m

Commissioner of Patents

1. A PROCESS FOR CASTING ACRYLIC SHEET COMPRISING POLYMERIZING AN ALKYLMETHACRYLATE MONOMER IN THE PRESENCE OF A FREE RADICAL CATALYST WHOSEDECOMPOSITION IS ACCELERATED BY A COMPLEXED BORON COMPOUND OF THEFORMULA Z-BR3 WHERE EACH R CAN BE HYDROGEN, HALOGEN OR HYDROCARBON ORHYDROCARBONOXY GROUP HAVING FROM 1 TO ABOUT 14 CARBON ATOMS OR -- OBR2GROUP AND Z IS A WEAKLY BASIC COMPLEXING AGENT HAVING AN IONIZATIONCONSTANT IN THE RANGE OF ABOUT 10**5 TO ABOUT 10**11 AND IN THE PRESENCEOF AT LEAST 33% BY WEIGHT INORGANIC FILLER MATERIAL HAVING A WATERSOLUBILITY LESS THAN 0.15 GRAM PER LITER, SAID MATERIAL BEINGSUFFICIENTLY DISPERSED AND DISTRIBUTED THROUGHOUT THE MONOMER TO SERVEAS AN EFFECTIVE HEAT SINK FOR THE EXOTHERMIC HEAT OF POLYMERIZATION.